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Monday, May 03, 2004

# Posted 7:23 PM by Patrick Belton  

WE MAY NOT BE ABLE TO SINGLE-HANDEDLY DUMB DOWN AMERICA, BUT BY GOD WE'LL TRY, AWARD: Goes to USA Today, for managing to combine stunning amounts of both condescension and needless confusion in this answer:
Q: What is the formula for converting pressure in millibars of pressure to inches of mercury?

You don't really need a formula. The "standard" atmospheric pressure at sea level is 29.92 inches of mercury, or 1013.2 millibars. In other words, these numbers are the same, but in different measurement systems. Anyway, if you see a pressure on a weather map of, say, 1016 millibars, you can convert to inches of mercury by multiplying by 29.92 and dividing by 1013.2 to come up with 30.00 inches of mercury.

Why? Think of the rules for cancellation. When you multiply by inches of mercury and divide by millibars, the millibars cancel out and you're left with inches of mercury. And, it's OK to do the multiplication and division because the numbers represent the same air pressure. A number divided by itself is 1 and when you multiply a number by 1 you get the original number. To go the other way from inches of mercury to millibars, you just divide by inches of mercury and multiply by millibars. This method is a good way to do all sorts of conversions without memorizing a bunch of formulas, as long as you know one equivalent set of numbers in the two systems.
Or, for those of you who got lost somewhere in that mess of USA Today-speak, you could alternatively just use (milibars) * 0.02953 = (inches of mercury).
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